ABSTRACT Bronchopulmonary Dysplasia or BPD is a chronic lung disease that results from interruption of normal in utero lung development by premature birth. We have shown that bioactive TGFbeta in the lungs of human preterm infants predicts severity of BPD, suggesting a possible role in its pathogenesis and arrested lung development. Another key signaling molecule with suggested role in pathogenesis of BPD is FGF10 which was recently found to be decreased significantly in BPD lungs. Our preliminary studies establish an operational link between FGF10 & TGFbeta through the Pten/PI3k/Akt/Erk pathway. We have further shown that FGF10 can protect lungs from TGF-beta&#8208;induced fibrosis in mice. This project will use simple genetic and molecular approaches to address the role of TGFbeta & FGF10 in pathogenesis of BPD. The logical basis for the current proposal rests on a number of preliminary, but important data that collectively, support the following overall hypothesis: HYPOTHESIS: We hypothesize that TGFbeta signaling via T&#61666;RII derails lung morphogenesis by inhibiting epithelial progenitor cell proliferation, mediated thru increased Pten, which leads to inhibition of PI3k/Akt/Erk pathway. We further hypothesize that FGF10 can protect the neonatal lung from hyperoxia/TGF&#61666;-mediated injury & BPD at least in part by countering the inhibitory effect of TGF&#61666;&#61472;on the PI3k/Akt/Erk pathway. The following specific aims will test the validity of the above hypothesis Specific Aim 1. To Determine the Precise Pathway via Which TGF&#61666;&#61472;Inhibits Epithelial Progenitor Cell Proliferation and Morphogenesis in both in vitro & in vivo Models. The availability of genetically engineered mice offers an unprecedented opportunity to elucidate the precise role of a key target of TGF&#61666;, Pten, & its signaling target, the PI3k/Akt/Erk pathway in both in vitro & in vivo settings. Specific Aim 2. To determine the Potential Role of TbetaRII in Epithelial & Mesenchymal Compartments of the Lung in Pathogenesis of Hyperoxia-Induced Hypoalveolization in Neonatal Mice (The mouse BPD Model). Mice carrying either Epithelial-&#8208; or Mesenchymal-&#8208;specific deletion of TbetaRII will be exposed to hyperoxia and the process of alveolization will be measured by state-&#8208;of-&#8208;the-&#8208;art technical approaches. Specific Aim 3. To Determine the Role of FGF10 in a Murine Model of Hyperoxia-Induced Hypoalveolization. We have shown that mesenchymal deletion of TbetaRII leads to increaseded FGF10. Remarkably regulated ectopic expression of Fgf10 in transgenic mice protects from bleomycin-&#8208;induced adult lung injury. In this aim, we will test the hypothesis that ectopic Fgf10 also protects from hyperoxia-&#8208;induced lung injury in neonatal transgenic mice. As in Specific Aim 1, the focus of the mechanisms in this aim will be the PI3k/Akt/Erk pathway.